Power conversion device

ABSTRACT

A power conversion apparatus is for converting polyphase ac power directly to ac power. A conversion circuit includes a plurality of first switching devices  311, 313, 315  and a plurality of second switching devices  312, 314, 316  connected, respectively, with the phases R, S, T of the polyphase ac power, and configured to enable electrical switching operation in both directions. There are provided a plurality of condensers  821˜826  connected with the conversion circuit. At least one of the condensers is provided, for each of the first switching devices and the second switching devices, between two of the phases of the polyphase ac power. It is possible to reduce a wiring distance between the condenser and the switching devices.

TECHNICAL FIELD

The present invention relates to a power conversion device or apparatusfor converting ac power of utility frequency or commercial powerfrequency, directly into desired ac power.

BACKGROUND ART

There is known a matrix converter as a power conversion apparatus forconverting ac power to ac power directly and efficiently with aconstruction requiring a smaller number of component parts and enablingsize reduction of the apparatus (Patent Document 1).

However, the routing or wiring distance of wires is long for connectingto switching means including IGBT (Insulated Gate Bipolar Transistor),in the above-mentioned matrix converter of earlier technology in whicheach of the phases (R phase, S phase, T phase) is provided with one offilter condensers forming a filter circuit, and the filter condensersare installed in a unit case.

PRIOR ART LITERATURE Patent Document(s) Patent Document 1: JP2006-333590A SUMMARY OF THE INVENTION

It is an object of the present invention to provide power conversiondevice or apparatus for reducing a wiring distance between filtercondensers and switching means.

A power conversion apparatus according to the present invention:

-   -   a conversion circuit including a plurality of first switching        devices connected, respectively, with phases of the polyphase ac        power, and configured to enable electrical switching operation        in both directions, and a plurality of second switching devices        connected, respectively, with the phases of the polyphase ac        power, and configured to enable electrical switching operation        in both directions; and a plurality of condensers connected with        the conversion circuit,    -   wherein at least one of the condensers is provided, for each of        the first switching devices and the second switching devices,        between two of the phases of the polyphase ac power        corresponding to each of the first switching devices and the        second switching devices.

According to the present invention, the filter condensers can be placednear the respective switching devices, so that it is possible to reducethe wiring distance between the filter condensers and the switchingdevices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an electric circuit diagram showing a power conversion systemto which one embodiment of the present invention is applied.

FIG. 2A is a plan view showing a power conversion apparatus according tothe embodiment of the present invention, in an intermediate state underan assembly process.

FIG. 2B is a plan view showing the power conversion apparatus accordingto the embodiment of the present invention, in an intermediate stateunder the assembly process.

FIG. 2C is a plan view showing the power conversion apparatus accordingto the embodiment of the present invention, in an intermediate stateunder the assembly process.

FIG. 2D is a side view showing the power conversion apparatus accordingto the embodiment of the present invention, in an intermediate stateunder the assembly process.

FIG. 3 is a view showing a layout of IGBTs and filter condensers of thepower conversion apparatus shown in FIG. 2, in a plan view and a sideview.

FIG. 4A is a plan view showing another layout of the IGBTs and filtercondensers shown in FIG. 3.

FIG. 4B is a side view of FIG. 4A.

FIG. 5 is a view showing still another layout of the IGBTs and filtercondensers shown in FIG. 3, in a plan view.

FIG. 6 is a view showing still another layout of the IGBTs and filtercondensers shown in FIG. 3, in a plan view.

FIG. 7 is an electric circuit diagram showing a power conversion systemto which another embodiment of the present invention is applied.

FIG. 8 is a view showing a layout of the IGBTs and filter condensersshown in FIG. 7, in a plan view and a side view.

FIG. 9 is a view showing another layout of the IGBTs and filtercondensers shown in FIG. 7, in a plan view and a side view.

MODE(S) FOR CARRYING OUT THE INVENTION

<<Outline of Power, Conversion System 1>>

First, FIG. 1 is used for illustrating the outline of a power conversionsystem to which an embodiment of the present invention is applied. Apower conversion system 1 of this example is a system to convertthree-phase ac power supplied from a three-phase ac power supply orpower source 2, directly to single-phase ac power, with a powerconversion apparatus or device 3 according to the embodiment of thepresent invention, to step up or down the single-phase ac power to anappropriate voltage with a transformer 4, and thereafter to convert theac power to dc power with a rectifier 5, and thereby to charge asecondary battery 6. There is further provided a smoothing circuit 7.

A filter circuit 8 is provided, in power conversion system 1 of thisexample, for attenuating higher harmonics for noise suppression for eachphase of output lines (R phase, S phase and T phase) to supply thethree-phase ac power from three-phase ac power supply or source 2.Filter circuit 8 of this example includes three filter reactors 81connected with the three phases R, S and T, respectively, and six filtercondensers or capacitors 82L, 82R connected among the three phases R, Sand T. A layout of filter condensers 82L, 82R (shown in FIGS. 3˜6, asfilter condensers 821˜836) is explained later.

In the power conversion system of this example, the three-phase ac poweris supplied through filter circuit 8, to power conversion apparatus 3,and converted to the signal-phase ac power. Power conversion apparatus 3of this example includes 6 bidirectional switching devices 31 arrangedin a matrix corresponding to the R, S and T phases. Hereinafter, areference numeral 31 is used, as a generic term, to denote one of thebidirectional switching devices generally, and reference numerals311˜316 are used to denote a specific one of the six bidirectionalswitching devices, as shown in FIG. 1.

Each of the bidirectional switching devices 31 of this example is anIGBT module including a semiconductor switching element in the form ofan IGBT (Insulated Gate Bipolar Transistor), and an anti-parallelfreewheel diode or flyback diode combined in an anti-parallelconnection. The construction of each bidirectional switching device 31is not limited to the construction shown in the figure. For example, itis optional to employ a construction including two reverse blocking IGBTelements in the anti-parallel connection.

A snubber circuit 32 is provided for each of bidirectional switchingdevices 31, to protect the corresponding bidirectional switching device31 from surge voltage generated with ON/OFF operation of thebidirectional switching device 31. Snubber circuit 32 is connected withthe input side and the output side of the corresponding bidirectionalswitching device 31 and formed by a combination of one snubber condenseror capacitor and three diodes. Hereinafter, a reference numeral 32 isused, as a generic term, to denote one of the snubber circuitsgenerally, and reference numerals 321˜326 are used to denote a specificone of the six snubber circuits, as shown in FIG. 1.

A matrix converter control circuit 9 is provided, in the powerconversion system 1 of this example, for ON/OFF control of each ofbidirectional switching devices 31 of power conversion apparatus 3.Matrix converter control circuit 9 receives, as inputs, a value of avoltage supplied from three-phase ac power source 2, a value of a dccurrent currently being outputted, and a value of a target currentcommand, controls the gate signal of each of bidirectional switchingdevices 31 in accordance with these inputs, adjusts the single-phase acpower outputted to transformer 4, and thereby obtains the dc powercorresponding to a target.

Transformer 4 increases or decreases the voltage of single-phase acpower obtained by conversion of power conversion apparatus 3, to apredetermined value. Rectifier 5 includes four rectifying diodes andconvers the single-phase ac power of the adjusted voltage into dc power.Smoothing circuit 7 includes a coil and a condenser or capacitor andsmooths pulsation included in the dc current obtained by therectification, into a condition closer to the dc current.

The thus-constructed power conversion system 1 of this example convertsthe three-phase ac power supplied from three-phase power supply 2,directly into the single-phase ac power with power conversion apparatus3, and convers the single-phase ac power into the dc power after theadjustment to a desired voltage. Thus, secondary battery 6 is charged.The power conversion system 1 is merely one example to which the powerconversion apparatus 3 according to the present invention is applied.The present invention is not limited to this example in which thepresent invention is applied to the power conversion system 1. Thepresent invention is applicable to other power conversion systems whenat least one of the power before conversion and the power afterconversion is polyphase ac power.

<<Layout of parts of Power Conversion Apparatus 3>>

FIGS. 2˜6 are views for illustrating the spatial layout or arrangementof parts constituting power conversion apparatus 3 shown in FIG. 1. Inthese figures, the same reference numerals are used for identical partsshown in FIG. 1 to show the correspondence in the figures.

FIG. 2 includes FIGS. 2A˜2D. FIG. 2A is a plan view showing anintermediate state during the assembly process, in which the sixbidirectional switching devices 31 (also referred to as the IGBTmodules) are mounted on an upper surface of a heat sink 10. FIG. 2B is aplan view showing an intermediate state during the assembly process, inwhich busbars are further mounted, for connecting terminals of thebidirectional switching devices 31. FIG. 2C is a plan view showing anintermediate state during the assembly process, in which, of the threediodes forming the snubber circuit 32, and the filter condensers 82 offilter circuit, the left side three filter condensers are mounted. FIG.2D is a side view showing the intermediate state during the assemblyprocess. Since constituent parts of power conversion apparatus 3 of thisexample are overlapped in the plan view, in the following explanation,main portions are shown in another drawing.

As shown in FIG. 2 and FIG. 3, each bidirectional switching device 31 ofthis example includes an input terminal, an output terminal and anintermediate or midpoint terminal between the two IGBTs arranged in apair, and the inpute terminal, output terminal and intermediate terminalare provided on the upper side of the module package. Among the sixbidirectional switching devices 311˜316 shown in FIG. 3, the left sideterminals of the three left side bidirectional switching devices 311,313 and 315 are input terminals, the right side terminals of the threeleft side bidirectional switching devices 311, 313 and 315 are outputterminals, and the central terminals of the three left sidebidirectional switching devices 311, 313 and 315 are intermediateterminals. Among the six bidirectional switching devices 311˜316 shownin FIG. 3, the right side terminals of the three right sidebidirectional switching devices 312, 314 and 316 are input terminals,the left side terminals of the three right side bidirectional switchingdevices 312, 314 and 316 are output terminals, and the central terminalsof the three right side bidirectional switching devices 312, 314 and 316are intermediate terminals. Gate terminals of bidirectional switchingdevices 31 are provided in another part of the module package andomitted in the figure.

As shown in FIG. 2 and FIG. 3, the six bidirectional switching devices311˜316 are fixed on the upper surface of heat sink 10, by fasteningmeans such as bolts. As shown in these figures, the six bidirectionalswitching devices 311˜316 are arranged in three pairs: a first pair ofbidirectional switching devices 311 and 312 disposed, respectively, onthe left and right sides of a center line CL, a second pair ofbidirectional switching devices 313 and 314 disposed, respectively, onthe left and right sides of the center line CL, and a third pair ofbidirectional switching devices 315 and 316 disposed, respectively, onthe left and right sides of the center line CL. In other words, thebidirectional switching devices 311 and 312 are disposed side by side,on the left and right side of center line CL, respectively, along theextending direction in which the three terminals (input terminal, outputterminal and intermediate terminals) of each bidirectional switchingdevice 31 are extended or arranged; the bidirectional switching devices313 and 314 are disposed side by side, on the left and right side ofcenter line CL, respectively, along the extending direction; and thebidirectional switching devices 315 and 316 are disposed side by side,on the left and right side of center line CL, respectively, along theextending direction. Hereinafter, this arrangement is also expressed as“juxtaposition, or parallel arrangement, with respect to center line CLor output lines P, N connecting the output terminals”. This arrangementis different from the arrangement shown in FIG. 5. The pairedbidirectional switching devices are two bidirectional switching devicesconnected with the same one of the R, S, T phases of the input line.

With this arrangement or juxtaposition including the bidirectionalswitching devices 311 and 312; 313 and 314; or 315 and 316 of each pairdisposed on the left and right sides of center line CL, it is possibleto employ a layout to draw out the output lines P and N (busbars 331 and332) in one direction at a minimum distance. Since influence of Lcomponent is increased by an increase of wiring outputting highfrequency ac power, the arrangement of this example can restrain theinfluence of the L component. This effect of the arrangement of thisexample is more advantageous as compared to the example shown in FIG. 5.Thus, the output lines P and N are almost straight up to transformer 4.

As mentioned before, the right end terminals of left side bidirectionalswitching devices 311, 313 and 315 on the left side of center line CLare all output terminals, and the left end terminals of left sidebidirectional switching devices 311, 313 and 315 are all inputterminals. The left end terminals of right side bidirectional switchingdevices 312, 314 and 316 on the right side of center line CL are alloutput terminals, and the right end terminals of right sidebidirectional switching devices 312, 314 and 316 are all inputterminals.

To the input terminals at the left ends of bidirectional switchingdevices 311, 313 and 315 on the left side of center line CL, the inputlines R, S and T of one branch branching off from the input lines ofthree-phase ac power supply 2 are connected in an inward directiontoward the center line CL. To the input terminals at the right end ofbidirectional switching devices 312, 314 and 316 on the right side ofcenter line CL, the input lines R, S and T of the other branch branchingoff from the input lines of three-phase ac power supply 2 are connectedin an inward direction toward the center line CL. The R phase isconnected to the input terminals of bidirectional switching devices 311and 312; the S phase is connected to the input terminals ofbidirectional switching devices 313 and 314; and the T phase isconnected to the input terminals of bidirectional switching devices 315and 316. The input lines R, S and Ton the left side are extended andconnected in the inward direction toward center line CL, and the inputlines R, S and T on the right side are also extended and connected inthe inward direction toward center line CL. With this connectingarrangement of the input lines, it is possible to decreases the distancein the left and right direction, of heat sink 10 as compared to thearrangement in the other example shown in FIG. 6.

In the configuration of FIG. 1, the input lines R, S and T extendingfrom three-phase ac power supply 2 to power conversion apparatus 3branch off at the position between the filter reactors 81 and the filtercondensers 82L and 82R. However, it is possible to employ aconfiguration in which the input lines R, S and T are divided into twobranches on the upstream side of filter reactors 81, and the filterreactors 81 are provided for each of the branches of the input lines R,S and T.

A busbar 331 forming an output line P of power conversion apparatus 3 isconnected with the right end output terminals of bidirectional switchingdevices 311, 313 and 315 on the left side of center line CL. A busbar332 forming an output line N of power conversion apparatus 3 isconnected with the left end output terminals of bidirectional switchingdevices 312, 314 and 316 on the right side of center line CL. Theforward ends of the busbars 331 and 332 are connected with transformer4. Busbars including these busbars 331 and 332 and busbars mentionedherein below are made of conductor such as copper, superior in theelectrical conductivity.

A busbar 333 connects the input terminals of bidirectional switchingdevices 311 and 312 paired with each other and disposed on the left andright sides of center line CL. A busbar 334 connects the input terminalsof bidirectional switching devices 313 and 314 paired with each otherand disposed on the left and right sides of center line CL. A busbar 335connects the input terminals of bidirectional switching devices 315 and316 paired with each other and disposed on the left and right sides ofcenter line CL. In the equivalent circuit shown in FIG. 1, the wiringscorresponding to the busbars are shown with the same reference numerals,respectively. These busbars 333˜335 are not essential for the functionof power conversion apparatus 3, and therefore, it is optional to omitthese busbars.

These busbars 333˜335 are arranged to intersect the busbars 331 and 332forming the output lines P and N as viewed in a plan view. However, asshown in the side view of FIG. 3, the busbars 333˜335 connecting theinput terminals are formed at a position higher than the busbars 331 and332, and thereby arranged to avoid interference therebetween with amultilevel crossing structure of overpass or underpass.

The filter condensers 82L and 82R provided between two of the phases canbe used in common by employing the arrangement in which thebidirectional switching devices 311 and 322 disposed on the left andright sides of center line in the first pair are connected, thebidirectional switching devices 313 and 324 in the second pair areconnected, and the bidirectional switching devices 315 and 326 in thethird pair are connected. Specifically, filter condenser 821 is providedbetween the R and S phases on the left side in FIG. 3, and filtercondenser 824 is provided between the R and S phases on the right sidein FIG. 3. The busbar 333 connects the input terminals of bidirectionalswitching devices 311 and 312 to which the R phase is inputted.Therefore, noises in the R phase of three-phase ac power supply 2 areremoved by cooperative filtering operation of the two filter condensers821 and 824. Consequently, it is possible to reduce the capacity of onefilter condenser and hence to reduce the sizes of the filter condensers.The same is applied to the S phase and the T phase.

The filter circuit in this example includes the six filter condensers821˜826 so arranged that three of the six filter condensers areconnected among the input lines on the left side of center line CL andthe remaining three are connected among the input lines on the rightside of center line CL, as shown in FIG. 3. The left side filtercondenser 821 is provided between the S phase and the R phase whichcorresponds to the input terminal of bidirectional switching device 311.Similarly, the left side filter condenser 822 is provided between the Tphase and the S phase which corresponds to the input terminal ofbidirectional switching device 313. The left side filter condenser 823is provided between the R phase and the T phase which corresponds to theinput terminal of bidirectional switching device 315. Similarly, theright side filter condenser 824 is provided between the S phase and theR phase corresponding to the input terminal of bidirectional switchingdevice 313. The right side filter condenser 825 is provided between theT phase and the S phase corresponding to the input terminal ofbidirectional switching device 314. The right side filter condenser 826is provided between the R phase and the T phase corresponding to theinput terminal of bidirectional switching device 316.

With the arrangement in which the six filter condensers 821˜826 arearranged so that three are on the left side of center line CL and theother three filter condensers are on the right side, for the sixbidirectional switching devices 311˜316 arranged so that three are onthe left side of center line CL and the other three switching devicesare on the right side, it is possible to reduce the distance or lengthof connection wire routing for each of filter condensers 821˜826 andbidirectional switching devices 311˜316.

In this example, the left three and the right three of filter condensers821˜826 are disposed on the outer sides of the region in which the sixbidirectional switching devices 311˜316 are formed, with respect tocenter line CL. Concretely, as shown in FIG. 2D, the left three and theright three of filter condensers 821˜826 are fixed on upper part of thebusbars. With the arrangement in which filter condensers 821˜826 are soarranged that the bidirectional switching devices 311˜316 are locatedbetween the left three filter condensers and the right three filtercondensers, it is possible to minimize the spacing between the left andright bidirectional switching devices 31 L and 31 R in the left andright direction. Therefore, it is possible to set the distance or lengthin the left and right direction, of heat sink 10 at a minimum value. Asa result, it is possible to reduce the size of heat sink 10 as comparedto the arrangement in another example shown in FIG. 4A.

The left three and the right three of filer condensers 821˜826 aremounted on the left and right sides of center line CL as shown in FIG. 2showing the plan view and side view of an actual apparatus.

Beforehand, the explanation is directed to the connection structure ofthe busbars. As shown in FIG. 2B, busbar 331 forms the output line Pconnecting the output terminals of bidirectional switching devices311,313 and 315 and leading to transformer 4. Busbar 332 forms theoutput line N connecting the output terminals of bidirectional switchingdevices 312,314 and 316 and leading to transformer 4. Busbar 333 is abusbar connecting the input terminals of bidirectional switching devices311 and 312, and including a first end portion which extends outwards ina leftward direction beyond the input terminal of bidirectionalswitching device 311 and which is connected with a busbar 336 to connectthe filter condenser 823, and a second end portion which extendsoutwards in a rightward direction beyond the input terminal ofbidirectional switching device 312 and which is connected with a busbar337 to connect the filter condenser 826 (cf. FIG. 2C and FIG. 3 for theconnection state of filter condensers 823 and 826). Busbars 336 and 337connected with both ends of busbar 333 are inclined with respect to aline connecting the input terminals of bidirectional switching devices311, 313 and 315, that is a line extending in an up and down directionas viewed in FIG. 2C.

Busbar 334 is a busbar connecting the input terminals of bidirectionalswitching devices 313 and 314, and including a first end portion whichextends outwards in the leftward direction beyond the input terminal ofbidirectional switching device 313 and which is connected with a busbar338 to connect the filter condensers 821 and 822, and a second endportion which extends outwards in the rightward direction beyond theinput terminal of bidirectional switching device 314 and which isconnected with a busbar 339 to connect the filter condensers 824 and 825(cf. FIG. 2C and FIG. 3 for the connection state of filter condensers821, 822, 824 and 825).

Busbars 338 and 339 connected with both ends of busbar 334 extend alongthe line connecting the input terminals of bidirectional switchingdevices 311, 313 and 315, that is the line extending in the up and downdirection as viewed in a left upper view(FIG. 2C?) of FIG. 2.

Busbar 335 is a busbar connecting the input terminals of bidirectionalswitching devices 315 and 316, and including a first end portion whichextends outwards in the leftward direction beyond the input terminal ofbidirectional switching device 315 and which is connected with a busbar340 to connect the filter condenser 823, and a second end portion whichextends outwards in the rightward direction beyond the input terminal ofbidirectional switching device 316 and which is connected with a busbar341 to connect the filter condenser 826 (cf. FIG. 2C and FIG. 3 for theconnection state of filter condensers 823 and 826). Busbars 340 and 341connected with both ends of busbar 335 are inclined with respect to theline connecting the input terminals of bidirectional switching devices311, 313 and 315, that is the line extending in the up and downdirection as viewed in FIG. 2C.

As shown in FIG. 2D, these busbars 333, 334 and 335 are connected withthe input terminals of bidirectional switching devices 311˜316 through aplurality of busbars 345 and 346, and disposed at a position or levelabove the busbars 331 and 332 forming the output lines P and N. Withthis arrangement, the busbars 333˜335 and the busbars 331 and 332 areseparated in the height or vertical direction with a predeterminedclearance without interference in the manner of grade separation ormultilevel crossing.

As shown by broken lines in FIG. 2C, filter condensers 821, 822 and 823are disposed on the outer side with respect to center line CL, andarranged so that the centers of filter condensers 821, 822 and 823 arelocated, respectively, at the apexes of a triangle (preferably anisosceles triangle or an equilateral or regular triangle) which isoriented so that one of the apexes is directed in the outward direction.With the arrangement of the three filter condensers 821, 822 and 823located at the apexes of the triangle, it is possible to set the wiringlengths among the condensers at minimum distances, to reduce the size ofpower conversion apparatus 3, and to attain tuning among the condensersproperly. Furthermore, with the arrangement in which the triangle is sooriented that one of the apexes of the triangle is directed in theoutward direction, it is possible to improve the balance of wiringconnecting to the condensers and to decrease the distance to each of thebusbars 333, 334 and 335, as compared to the arrangement in which one ofthe apexes of the triangle is directed in the inward direction,

Filter condenser 821 connected between the R phase and S phase ismounted on the upper surface of a busbar 342. Filter. condenser 822connected between the S phase and T phase is mounted on the uppersurface of a busbar 343. These two busbars 342 and 343 are inclined withrespect to a line connecting the input terminals of bidirectionalswitching devices 311, 313 and 315, that is, a line extending in the upand down direction in FIG. 2C. Moreover, these two busbars 342 and 343are extended across the line connecting the input terminals ofbidirectional switching devices 311, 313 and 315, that is, the lineextending in the up and down direction in FIG. 2C, and connected withbusbars 333, 342 and 335. Filter condensers 824 and 825 on the rightside of center line CL are arranged symmetrically with respect to centerline CL.

With the arrangement in which busbars 342 and 343 are inclined withrespect to the line connecting the input terminals of bidirectionalswitching devices 311, 313 and 315, it is possible to make the wiringdistance equal to the wiring distance of the filter condenser 823connected between the R phase and T phase, as much as possible.Therefore, it is possible to attain tuning among filter condensers 821,822 and 823. Moreover, with the arrangement in which busbars 342 and 343are provided across the line connecting the input terminals ofbidirectional switching devices 311, 313 and 315, it is possible toreduce the connection distances of filter condensers 821 and 822 withbusbars 333, 334 and 335, and hence it is possible to reduce the size ofpower conversion apparatus 3.

With the arrangement in which each of the filter condensers 821˜826 isdisposed on the upper surface of the busbars, namely the arrangement inwhich the bidirectional switching devices 311˜316 are disposed on oneside of the busbars, and the filter condensers 821˜826 are on theopposite side of the busbars, the design freedom or flexibility oflayout of filter condensers 821˜826 is increased.

Filter condenser 823 connected between the R phase and T phase ismounted on the upper surface of a busbar 344 connected between busbars336 and 340. This busbar 344 is disposed so that busbar 344 is parallelto the line connecting the input terminals of bidirectional switchingdevices 311,313 and 315.

Following is explanation on an implementing example of three diodes andone snubber condenser or capacitor forming one of the snubber circuits32 shown in FIG. 1. In the case of the snubber circuit 321 ofbidirectional switching device 311, for example, as shown in FIG. 1, afirst terminal of snubber circuit 321 is connected with the inputterminal of bidirectional switching device 311, a second terminal ofsnubber circuit 321 is connected with the intermediate terminal ofbidirectional switching device 311, and a third terminal is connectedwith the output terminal of bidirectional switching device 311.Therefore, as shown in FIGS. 2C and 2D, the three diodes are fixed andconnected, respectively, with brackets 351˜356 which are made ofconductor and connected with the intermediate terminals of bidirectionalswitching devices 31 L and 31 R. FIG. 2D shows only the bracket 355.

In this example, the conversion system uses a relatively large sizedelectrolytic condenser for the snubber condensers, and employs a snubbercondenser 327 common to the six snubber circuits 321˜326 (cf. FIG. 3).Busbars 347 and 348 for connecting this snubber condenser 327 and thethree diodes are formed to extend, between the busbars 331 and 332forming the output lines P and N, in the same direction as the outputlines.

As shown in FIG. 2D and FIG. 3, the two busbars 347 and 348 connectedwith snubber condenser 327 are fixed at a level higher than the busbars331 and 332 forming the output lines P and N, and lower than the busbars333,334 and 335. These two busbars 347 and 348 are supported by heatsink 10 or a base (not shown) other than heat sink 10. It is optional toprovide insulating coating on the surfaces of busbars 347 and 348 toprevent short-circuit with busbars 333,334 and 335.

As to the layout of busbar 311 and 312 forming output lines P and N andbusbars 347 and 348 leading to snubber condenser 327, the disposition ofbusbars 347 and 348 between busbars 311 and 312 makes it possible toreduces the wiring distances of output lines P and N and the wiringdistances to snubber condenser 327. Moreover, the setting of busbars 347and 348 at the position higher than busbar 311 and 312 makes it possibleto reduce the distances from the diodes of snubber circuits 321˜326.

According to this embodiment, it is possible to provide followingadvantages.

1) To the six bidirectional switching devices 311˜316, three devicesbeing on one of the left and right sides of center line CL, and theother three devices being on the other side, the six filter condensers821˜826 are disposed so that three of the six filter condensers aredisposed on the left side of center line CL to the three devices on theleft side, and the remaining three filter condensers are disposed on theright side of center line CL to the right three bidirectional switchingdevices. Therefore, it is possible to reduce the routing or wiringdistances of filter condensers 821˜826 and bidirectional switchingdevices 311˜316.

2) In this example, the pair of bidirectional switching devices 311 and312, the pair of bidirectional switching devices 313 and 314, and thepair of bidirectional switching devices 315 and 316 are arranged so thatthe two devices of each pair are arranged side by side on the left andright sides of center line CL, respectively. This layout makes itpossible to draw out the output lines P and N (busbars 331 and 332) inone direction shortly. Therefore, the layout of this example canrestrain the influence of the L component or inductance though a longerwire for outputting high frequency ac power would be susceptible to theinfluence of the L component.

3) In this example, the three of filter condensers 821˜826 on the leftside and the other three filter condensers on the right side aredisposed on the outer sides of the region in which the six bidirectionalswitching devices 311˜316 are provided, with respect to center line CLso that the region of the bidirectional switching devices is locatedbetween the three filter condensers on the left side and the other threefilter condensers on the right side. Therefore, it is possible tominimize the spacing, in the left and right direction, between the leftside bidirectional switching devices 31 L and the right sidebidirectional switching devices 31 R. Consequently, it is possible toset the distance or dimension of heat sink 10 in the left and rightdirection at a minimum distance, and hence to reduce the size of heatsink 10.

4) In this example, busbars 333,334 and 335 connect the input terminalsof bidirectional switching devices 311 and 312 arranged on the left andright side of center line CL in a pair, the input terminals ofbidirectional switching devices 313 and 314 arranged on the left andright side of center line CL in a pair, and the input terminals ofbidirectional switching devices 315 and 316 arranged on the left andright side of center line CL in a pair, respectively. Therefore, filtercondensers 82L and 82R provided between the phases can be utilized forcommon use. Consequently, it is possible to reduce a capacity of eachfilter condenser and hence to reduce the size of the filter condensers.

5) In this example, to the input terminals of bidirectional switchingdevices 31 L, the left side input lines R, S and T are extended in theinward direction toward center line CL. Similarly, to the inputterminals of bidirectional switching devices 31 R, the right side inputlines R, S and T are extended in the inward direction toward center lineCL. Therefore, it is possible to reduce the distance or dimension ofheat sink 10 in the left and right direction.

6) In this example, filter condensers 821˜826 are disposed on the upperside of the busbars. In other words, the bidirectional switching devices311˜316 are disposed on one side of the busbars, and the filtercondensers 821˜826 are disposed on the other side of the busbars.Therefore, the freedom of layout design of filter condensers 821˜826 isincreased.

7) In this example, as to the arrangement of busbars 311 and 312 formingoutput lines P and N and busbars 347 and 348 to snubber condenser 327,the busbars 347 and 348 are disposed between busbars 311 and 312.Therefore, it is possible to reduce the distances including thedistances of output lines P and N and the wiring distance to snubbercondensers 327.

8) In this example, the busbars 347 and 348 are disposed at the positionhigher than busbars 311 and 312. Therefore, it is possible to reduce thedistances from the diodes of snubber circuits 321˜326.

9) In this example, the three filter condensers 821,822 and 823 arepositioned at the apexes of a triangle, respectively. Therefore, it ispossible to minimize the wiring distances among the condensers, toreduce the size of power conversion apparatus 3, and to achieve tuningamong the condensers.

10) In this example, the three condensers positioned so as to form atriangle are arranged so that one apex of the triangle is directed inthe outward direction. Therefore, it is possible to improve the balanceof wiring connected with the condensers as compared to the arrangementin which one apex is directed in the inward direction, and to reduce thedistance to each of busbars 333, 334 and 335.

11) In this example, the busbars 342 and 343 are inclined with respectto the line connecting the input terminals of bidirectional switchingdevices 311, 313 and 315. Therefore, it is possible to make the wiringdistance equal to the wiring distance of the filter condenser 823connected between the R phase and T phase, as much as possible.Therefore, it is possible to attain tuning among filter condensers 821,822 and 823.

12) In this example, the busbars 342 and 343 are provided across theline connecting the input terminals of bidirectional switching devices311, 313 and 315. Therefore, it is possible to reduce the connectiondistances of filter condensers 821 and 822 with busbars 333, 334 and335, and hence it is possible to reduce the size of power conversionapparatus 3.

<<Other Embodiments>>

According to the present invention, variations and modifications arepossible, besides the preceding embodiment. Following is explanation onvariation examples according to the present invention. However, there isno intention of limiting the present invention to the above-mentionedembodiment, and following embodiments. Members used in theabove-mentioned embodiment are given the same reference numerals andexplanation is omitted appropriately.

In the above-mentioned embodiment, as shown in FIG. 3, the left sidethree filter condensers 82L and the right side three filter condensers82R are disposed, respectively, on the outer sides of bidirectionalswitching devices 311, 313 and 315, and on the outer side ofbidirectional switching devices 312, 314 and 316 with respect to centerline CL as the center. However, as shown in FIGS. 4A and 4B, it ispossible to place the left side three filter condensers 82L and theright side three filter condensers 82R, between the bidirectionalswitching devices 311, 313 and 315 on the left side of center line CLand the bidirectional switching devices 312, 314 and 316 on the rightside of center line CL.

Moreover, in the above-mentioned embodiment, as shown in FIG. 3, thebidirectional switching devices 311, 313 and 315 are disposed on theright side of center line CL, and the bidirectional switching devices312, 314 and 316 are disposed on the right side of center line CL.However, it is possible to employ an arrangement in which, as shown inFIG. 5, the bidirectional switching devices 311, 313 and 315 and thebidirectional switching devices 312, 314 and 316 are disposed along thecenter line CL.

In the above-mentioned embodiment, as shown in FIG. 3, the threebidirectional switching devices 311, 313 and 315 are disposed on theleft side of center line CL, the three bidirectional switching devices312, 314 and 316 are disposed on the right side of center line, and theinput terminals and the output terminals of these six bidirectionalswitching devices 311˜316 are arranged symmetrically with respect tocenter line CL in a manner of line symmetry or reflection symmetry.However, as shown in FIG. 6, it is possible to employ an arrangement inwhich the three bidirectional switching devices 311, 313 and 315 aredisposed on the left side of center line CL, the three bidirectionalswitching devices 312, 314 and 316 are disposed on the right side ofcenter line, and the input and output terminals of the left side threebidirectional switching devices 311, 313 and 315 and the input andoutput terminals of the right side bidirectional switching devices 312 m314 and 316 are arranged in the same manner. In this case, the two setof the input lines R, S and T are extended in the same direction (in therightward direction in the illustrated example) and connected with theinput terminals of the respective bidirectional switching devices.

Moreover, in the above-mentioned embodiment, as shown in FIG. 3, filtercondensers 821˜826 are provided between two phases so that each of thesix bidirectional switching devices 311˜316 corresponds uniquely to oneof the six filter condensers. However, as shown in FIG. 7, it ispossible to employ an arrangement in which filter condensers 821˜826 areprovided between two phases so that each of the six bidirectionalswitching devices 311˜316 corresponds uniquely to a plurality of filtercondensers (two of filter condensers in the illustrated example).

In this case, the filter condensers may be disposed in a center regionof the power conversion apparatus 3 as shown in FIG. 8, or may bedisposed on the outer sides of power conversion apparatus 3, as shown inFIG. 9. In the case of the arrangement in which the filter condensersare disposed in the center region of the power conversion apparatus 3 asshown in FIG. 8, it is possible to utilize free space and hence torestrain or reduce the size of power conversion apparatus 3 as much aspossible.

The bidirectional switching devices 311,313 and 315 correspond to afirst switching device or element in the claims of the presentinvention, and the bidirectional switching devices 312,314 and 316correspond to a second switching device or element in the claims of thepresent invention. The power conversion apparatus 3 corresponds to aconversion circuit in the claims of the present invention. The filtercondensers 821˜826,831˜836 correspond to condensers in the claims of thepresent invention. The busbars 331 and 332 corresponds to an output linein the claims of the present invention.

1.-6. (canceled)
 7. A power conversion apparatus for convertingpolyphase ac power directly to ac power, the power conversion apparatuscomprising: a conversion circuit including a plurality of firstswitching devices connected, respectively, with phases of the polyphaseac power, and configured to enable electrical switching operation inboth directions, and a plurality of second switching devices connected,respectively, with the phases of the polyphase ac power, and configuredto enable electrical switching operation in both directions; and aplurality of condensers connected with the conversion circuit; at leastone of the condensers being provided, for each of the first switchingdevices and the second switching devices, between two of the phases ofthe polyphase ac power corresponding to each of the first switchingdevices and the second switching devices; wherein a plurality of inputside busbars corresponding, respectively, to the phases of the polyphaseac power are arranged side by side with each other; each of the busbarsconnects input terminals of one of the first switching devices and oneof the second switching devices corresponding to one of the phases, witheach other; and at least one of the condensers is disposed at a firstportion of each of the busbars, near the input terminals of the firstswitching devices, between two of the phases of the polyphase ac power,and at least one of the condensers is disposed at a second portion ofeach of the busbars, near the input terminals of the second switchingdevices, between two of the phases of the polyphase ac power.
 8. Thepower conversion apparatus as recited in claim 7, wherein the firstswitching devices and the second switching devices are arranged, as aspatial arrangement, side by side with an output line of the conversioncircuit in a form of a parallel arrangement.
 9. The power conversionapparatus as recited in claim 7, wherein output terminals of one of thefirst switching devices and one of the second switching devicescorresponding to one of the phases are arranged side by side in a pair;and wherein the condensers are disposed, as a spatial arrangement, on anouter side of the output terminals of the first switching devices andthe second switching devices arranged in a pair.
 10. The powerconversion apparatus as recited in claim 8, wherein output terminals ofone of the first switching devices and one of the second switchingdevices corresponding to one of the phases are arranged side by side ina pair; and wherein the condensers are disposed, as a spatialarrangement, on an outer side of the output terminals of the firstswitching devices and the second switching devices arranged in a pair.11. The power conversion apparatus as recited in claim 7, wherein thecondensers connected with the first switching devices and the condensersconnected with the second switching devices, are connected with eachother.